Now that the main dialog is included in an iframe, we have to communicate
with the iframe from the parent to give to the iframe the good commands.
The structure of sendMessage/receiveMessage come from the Lightning project.
Especially the sendMessage() function which send command with the good event id
(needed for tab view).

Fix javascript code to:
* avoid removing event listener
* avoid using try/catch without need
* avoid to reset current set of items, but instead add back attachment
if not already in toolbar and url attachment is there

This code was the same than the original Lightening code contained in
chrome://messenger/content/messenger.xul
Exchangecalendar has nothing added and the overlay is bugged:
* it didn't overlay the context menu in the attendee tab on the
bottom of the dialog
* it didn't display days and times in the header of attendee dialog